Method for forming an STI feature to avoid acidic etching of trench sidewalls

Abstract

A method for forming a shallow trench isolation feature to avoid acidic etching of trench sidewalls including providing a semiconductor substrate having an overlying silicon nitride layer; photolithographically patterning the silicon nitride layer to expose a portion of the silicon nitride layer; anisotropically etching through a thickness of the portion of the silicon nitride layer to form a hardmask opening exposing a portion of the semiconductor substrate; blanket depositing a polymer layer according to a plasma deposition process including at least partially covering the sidewalls and bottom portion of the hardmask opening; and, anisotropically etching a trench opening through a thickness portion of the semiconductor substrate according to the hardmask opening.

What is claimed is:  
     
       1. A method for forming a shallow trench isolation feature to avoid acidic etching of trench sidewalls comprising the steps of: 
       providing a semiconductor substrate having an overlying silicon nitride layer;  
       photolithographically patterning the silicon nitride layer to expose a portion of the silicon nitride layer;  
       plasma etching through a thickness portion of the silicon nitride layer to form a hardmask opening exposing a portion of the semiconductor substrate;  
       in-situ blanket depositing a polymer layer according to a plasma deposition process comprising substantially filling the hardmask opening; and,  
       in-situ plasma etching a trench opening through a thickness portion of the semiconductor substrate through the hardmask opening such that the trench opening is formed having a width less than the hardmask opening.  
     
     
       2. The method of  claim 1 , wherein the semiconductor substrate comprises at least one of single crystalline silicon and polycrystalline silicon. 
     
     
       3. The method of  claim 1 , wherein the step of blanket depositing a polymer layer comprises at substantially filling the hardmask opening excepting keyhole formation. 
     
     
       4. The method of  claim 1 , wherein the plasma deposition process comprises supplying at least one fluoro-hydrocarbon to form a plasma for depositing the polymer layer. 
     
     
       5. The method of  claim 4 , wherein the at least one fluoro-hydrocarbon comprises fluoro-hydrocarbons with a fluorine to carbon ratio is equal to or less than about 3. 
     
     
       6. The method of  claim 5 , wherein the at least one fluoro-hydrocarbon comprises CH 2 F 2 . 
     
     
       7. The method of  claim 1 , wherein the trench opening comprises a width less than the width of the hardmask opening by about 10 to about 100 nanometers. 
     
     
       8. The method of  claim 6 , wherein the trench opening is anisotropically etched such that trench corners including a top and bottom portion of the trench opening are partially rounded having a radius of curvature. 
     
     
       9. The method of  claim 1 , further comprising the step of carrying out a plasma ashing process in-situ following the step of in-situ plasma etching a trench opening to remove the polymer layer to form a recessed area exposing the semiconductor substrate surrounding the trench opening having a combined width of about 10 to about 100 nanometers. 
     
     
       10. The method of  claim 5 , wherein the fluoro-hydrocarbons include at least one member selected from the group consisting of CHF 3 , C 5 F 8  and C 2 F 6  and CH 2 F 2 . 
     
     
       11. A method of forming a shallow trench isolation opening to avoid roughening trench sidewalls in a wet acidic etching process comprising the steps of: 
       providing a semiconductor substrate having an overlying silicon nitride layer;  
       photolithographically patterning the silicon nitride layer to expose a portion of the silicon nitride layer;  
       plasma etching through a thickness of the portion of the silicon nitride layer to form a hardmask opening exposing a portion of the semiconductor substrate;  
       in-situ blanket depositing a polymer layer according to a plasma deposition process comprising covering the sidewalls and bottom portion of the hardmask opening such that the sidewall portions of the polymer at least partially coalesce; in-situ plasma etching a trench opening through a thickness portion of the semiconductor substrate through the hardmask opening the trench opening formed to have a trench opening width less than a width of the hardmask opening; and,  
       in-situ plasma ashing to remove polymer materials including the polymer layer to form a recessed area exposing the semiconductor substrate surrounding the trench opening.  
     
     
       12. The method of  claim 11 , wherein the semiconductor substrate comprises at least one of single crystalline silicon and polycrystalline silicon. 
     
     
       13. The method of  claim 11 , wherein the at least one fluoro-hydrocarbon comprises fluoro-hydrocarbons with a fluorine to carbon ratio is equal to or less than about 3. 
     
     
       14. The method of  claim 13 , wherein the at least one fluoro-hydrocarbon comprises CH 2 F 2 . 
     
     
       15. The method of  claim 11 , wherein the recessed area comprises a combined width of about 10 to about 100 nanometers. 
     
     
       16. The method of  claim 11 , wherein the trench opening is plasma etched such that trench corners including a top and bottom portion of the trench opening are partially rounded having a radius of curvature. 
     
     
       17. The method of  claim 13 , wherein the fluoro-hydrocarbons include at least one member selected from the group consisting of CHF 3 , C 5 F 8  and C 2 F 6  and CH 2 F 2 .